If it is a standard AR-15 lower! An AR-15 lower is an AR-15 Lower. It would be good to attach a picture so we see it. A standard AR-15 Lower is the same for all the following whether it has a 5.56/223, 6.8 SPC, 6.5 Grendel, 6. 450 Bushmaster,458 SOCOM, 300 Blackout, 204, or 762X39 Upper on it. The only thing that changes is the upper due to the barrel (Cal.) the bolt and or the magazine it requires in most cases. If you are going to the 6.8 on your lower there should be no problem at all.